Generally, X-ray sources are conventionally X-ray tubes and use a kind of vacuum tube to emit electrons accelerated under high voltage. The emitted electrons collide with a metal target, thus creating X-rays. According to their methods of creating X-rays, the X-ray sources are classified into hot cathode X-ray tubes and cold cathode X-ray tubes.
However, the filament-type X-ray tube used in such an X-ray source is disadvantageous in that the volume thereof is required to be large in order to emit a significant number of electrons. Given this, recently, a synchrotron (a particle accelerator in which a magnetic field and the number of vibrations of an electric oscillator vary with time so that the radius of a charged particle that is in a circular motion is maintained constant), a laser plasma accelerator which uses a high-powered laser and a solid target, and a thermionic electron emission device or the like have been used as electron emitting sources.
These conventional X-ray sources have the advantage of high average output power. However, high voltage is required for high output power, and when high voltage is rapidly applied to an anode electrode of an X-ray source, heat generated from the anode electrode overheats the X-ray source, thus damaging the entirety of the X-ray machine.
That is, when electrons emitted from an emitter collide with a metal plate of the anode electrode, heat of 2000° C. or more is generally generated. If the anode electrode is made of copper, it is melted by the heat. In the case of tungsten or molybdenum, the temperature is almost close to the melting point thereof.
Thereby, the vacuum of the X-ray source which emits X-rays is destroyed, and high current is generated. As a result, the X-ray machine may malfunction.
Furthermore, the amount of radioactivity of X-rays emitted from the X-ray source increases in proportion to the voltage supplied to the X-ray source. In other words, an excessive amount of radiation is discharged, whereby the degree of radiation exposure of an X-ray technician or the target to be tested may be severe.
Particularly, if X-rays leak from areas other than a cathode electrode, the emitter, the anode electrode, a gate electrode or a focusing electrode, which are the parts involved in the emission of X-rays, the X-ray technician may be inadvertently exposed to radiation.
Moreover, conventional X-ray light sources are problematic in that because energy of the accelerated electrons is not uniform, the quality of generated electron beams or X-rays is very low, and it is impossible to provide an electron emission device in a satisfactory size of Because the degree of the spread of initial electron emission is comparatively large, there is a disadvantage in that the size of the focusing electrode and the gate electrode are increased.